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    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
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<body>
    <!-- 1，闰年判断。 -->
    <script>
        var year =prompt('请输入年份：');
        if(year%4==0&&year%100!=0||year%400==0){
            alert('是闰年！');
        }else{
            alert('不是闰年！');
        }
    </script>
</body>
</html>